Indoor water heaters of the domestic type usually comprise an upright generally cylindrical body including a tank for holding a quantity of water to be heated. A burner for natural gas or other gaseous fuel is disposed within a combustion chamber which is associated with the lower region of the water heater tank to conduct the heat of combustion to the water contained in the tank. The combustion chamber includes a combustion air inlet opening and a flue gas outlet opening. A flue pipe extends from the flue gas outlet opening to a position at the exterior of the water heater body where a connection is made between the flue pipe and a chimney or other passageway leading to the outdoor atmosphere. The flue pipe usually extends through the tank of water in order to conduct additional heat into the water from the flue gases.
A particular type of water heater employs an atmospheric burner to provide the heat of combustion at the combustion chamber. An atmospheric burner is an assembly at the terminal end of a fuel supply pipe which includes an air inlet and one or more flame apertures downstream from the air inlet. The flow of gaseous fuel to the burner draws surrounding atmospheric combustion air through the inlet to produce a mixture therewith which is ignited to burn upon exiting a flame aperture. The air inlet is often adjustable by rotation of a slotted disc or sleeve over an opening in the fuel supply pipe. In a water heater, the air inlet portion of the atmospheric burner defines in whole or in part the combustion air inlet opening which communicates the combustion chamber with the atmosphere of the room in which the heater is located. The flue pipe in such heaters extends vertically from the flue gas outlet opening at the combustion chamber directly to an open end at the top of the water heater body. A conical vent hood having an upper and lower open end is supported on brackets in a position raised above the top surface of the water heater body and received coaxially over the open end of the flue pipe to define an open annular space between the flue pipe and the lower end of the conical vent hood. The upper end of the vent hood is connected to a conduit leading to a chimney or other access to the outdoor atmosphere.
Combustion of the gaseous fuel at the atmospheric burner derives necessary oxygen from the combustion air surrounding the burner. Operation of the water heater is vented by means of a natural draft developed by the heat of combustion at the atmospheric burner. Room air is drawn into the combustion air inlet opening at the combustion chamber as the heat of combustion causes flue gases and heated combustion air to flow through the flue gas outlet opening and upwardly through the flue pipe to the chimney connection.
Atmospheric burner water heaters of this type suffer from several disadvantages. The greatest disadvantage arises in the use of room air for combustion air at the burner. Use of room air inefficiently wastes the energy expended to heat, cool, or humidify that air since it is wastefully driven out of the building with the exhaust of flue gases. A further loss of room air occurs through the open arrangement of the vent hood over the flue pipe which permits room air to pass through the annular space therebetween and upwardly to the chimney with the rising flue gases. Another disadvantage is that the heated interior components of the water heater cause a residual convective flow to proceed through the water heater between intermittent operations of the burner. This not only wastes room air being drawn in through the combustion chamber inlet opening, but also wastes heat which is consequently drawn out of the heated components and the stored quantity of water by the residual convective flow. Furthermore, a draft of room air out of the building through the water heater tends to cause a corresponding draft of outdoor air into the building through cracks or other spaces in door and window frames to further disrupt heating or air conditioning systems.
Another type of domestic indoor water heater employs a power burner to provide the heat of combustion. A power burner is a device for providing a mixture of gaseous fuel and combustion air which is calculated to increase the efficiency of fuel consumption. A water heater system employing a power burner generally comprises a fluid pressure regulating device, a gas valve adapted to direct a pressurized flow of fuel from a source to the pressure regulating device, and a centrifugal blower in a housing adapted to cause a pressurized flow of combustion air into the pressure regulating device. The pressure regulating device is adapted to provide a predetermined mixture of fuel and air and has an outlet therefor leading into the combustion chamber of the water heater. The flue pipe in such heaters may extend from the combustion chamber outlet opening through the tank of water in either a straight or an non-linear configuration to a position at the exterior of the water heater where a connection is made to a chimney or conduit extending to the outdoor atmosphere. A combustion air inlet conduit may be provided to extend from the outdoor atmosphere to the combustion chamber inlet opening to complete a direct vent system which vents the combustion chamber to the outdoor atmosphere in isolation from indoor room air.
Operation of a power burner water heater system commences when a water temperature thermostat signals the gas valve to supply fuel to the power burner. The centrifugal blower usually begins to supply combustion air to the power burner in response to the flow of gaseous fuel. As the mixture of air and fuel is burned, the system is vented by the force of air pressure induced by the centrifugal blower. The blower may be placed downstream from the combustion chamber in line with the expulsion of flue gases, in which case it is referred to as an induced draft blower, or it may be placed upstream of the combustion chamber in line with the incoming combustion air, in which case it is termed a forced draft blower. In either case, the blower is arranged to direct a flow of combustion air to the power burner system, and a corresponding flow of flue gases and heated combustion air from the combustion chamber through the flue pipe and the outlet conduit to the outdoor atmosphere.
Water heaters having power burners also suffer from several disadvantages. A complex control system is required to cause the thermostat to operate the gas valve, and to cause the blower to operate in response to fuel flow at the gas valve or the pressure regulating device. The pressure regulating device is itself a complex component requiring precise adjustment upon installation, and often requires periodic maintenance of an equally precise nature. Such precision is required for it to mix fuel and air in response to both the blower air pressure and the supplied fuel pressure. Power burner systems also disadvantageously consume electricity to drive the centrifugal blower and to operate the pressure regulator in addition to the consumption of gaseous fuel. Centrifugal blowers consume greater amounts of electrical energy than do simple propeller fans, but are used in order to meet the pressure requirements of the power burner as well as to drive the venting flow. Furthermore, if a direct vent system is not provided and combustion air is thus drawn from the surrounding room instead of from the outdoor atmosphere, the higher pressure requirements of the power burner system will cause an even greater loss of conditioned room air than is experienced in the natural draft atmospheric burner systems described above.
It is sometimes desirable to employ the heated water from the water heater to heat room air in the building in which the water heater is installed. Water heaters having power burner systems are known to have been adapted for this purpose. Heated water is pumped from the tank in the water heater to a coil exposed to the room air, and is returned to the tank in a cycle separate from the ordinary flow of hot and cold potable water through the water heater and associated plumbing. The coil is associated with an existing space heating system at an air duct or radiator. Such attempts to provide a combination water heater-space heater thus require plumbing connections to be made through the room space between the water heater and the existing space heating system, and disadvantageously occupy and limit available room space in utility rooms or other similarly cramped indoor locations where these appliances must be installed.
Disadvantages common to both atmospheric burner and power burner systems include the location of the gas valve and associated components at the exterior of the water heater body. Exposure of these components could subject them to damage upon shipment or installation, or to improper adjustment by untrained personnel after installation. These components also present a somewhat inappropriate appearance for a finished basement or other common household location of a water heater.
Known water heaters are thus seen to fail to provide a venting system which efficiently operates in isolation from indoor room air without requiring the use of complex electrical components such as fluid pressure regulators and energy consuming centrifugal blowers, or to provide an unobtrusive and compact arrangement of components to serve as a combination water heater and space heater.